1. Field of the Invention
The present invention relates to a method of forming a capacitor of an integrated circuit device, and more particularly, to a method of forming a capacitor of an integrated circuit device having a diffusion barrier layer formed of an Al2O3 layer in a single atomic layer deposition method and a dielectric layer formed of a Ta2O5 layer on the diffusion barrier layer.
2. Description of the Related Art
As the degree of integration of semiconductor memory devices such as dynamic random access memory (DRAM) increases, the size of each cell area is decreased, but all components needed to perform the functions of each cell must still fit within the reduced cell area. Accordingly, efforts have been made to increase a cell capacitance in a given cell area.
As is well known to those skilled in the art, there are various methods to increase the cell capacitance, such as increasing the effective area of a capacitor, reducing the thickness of a dielectric layer, and increasing the dielectric constant of the dielectric layer.
Recently, a metal oxide layer such as aluminum oxide and tantalum oxide (Ta2O5) is used as the dielectric layer instead of the conventional dielectric layer such as a silicon oxide layer or a nitride layer. The advantage in using a dielectric layer consisting of Ta2O5 is because of its higher dielectric constant of about 26.
However, a surface of the tantalum oxide layer is easily reduced to a tantalum rich phase, thereby being unstable in the surface of the tantalum layer. And a SiO2 layer is easily formed before or after depositing the tantalum oxide layer at the interface between the tantalum oxide layer and the polysilicon layer provided as a storage electrode and a plate electrode. To reduce unstable characteristics, a rapid thermal nitridation is performed on the storage electrode formed of the polysilicon layer to form a nitride layer comprised of Si3N4 before depositing the tantalum oxide layer, thereby preventing forming the oxidation of the polysilicon layer.
However, if the nitride layer is formed non-uniformly or the growth of the nitride layer is insufficient due to a native oxide layer that is formed after cleaning the nitride layer, there is a problem in that the dielectric layer consisting of Ta2O5 will not be properly deposited.
On the other hand, even though the tantalum oxide layer is deposited on a semiconductor substrate via a chemical vapor deposition, oxygen vacancy appears in the dielectric layer. Therefore, an UV-O3 treatment is typically performed to compensate for the oxygen vacancy during the chemical vapor deposition. Furthermore, the tantalum oxide layer is crystallized under an oxygen atmosphere by a heat treatment to increase the dielectric constant after performing the deposition.
When the tantalum oxide layer is performed the heat treatment under the oxygen atmosphere during the deposition or after the deposition, a storage electrode is also oxidized by a reaction with oxygen. The generation of the oxide layer increases the thickness of the dielectric layer of the capacitor, thereby reducing the capacitance of the capacitor of the semiconductor memory cell.
U.S. Pat. No. 5,316,982 issued to Taniguchi, et al. on May 31, 1994 discloses a capacitor of a semiconductor device having a lower electrode comprised of a Si-containing material, an aluminum oxide film formed on the surface of the lower electrode, a dielectric film of Ta2O5 formed on the aluminum oxide film, and an upper electrode on the dielectric film. According to Taniguchi, the aluminum oxide film is used for preventing a silicon oxide film from being formed on an interface between the poly-silicon film and the dielectric film of Ta2O5. This purportedly improves leakage current characteristics of the dielectric film of Ta2O5. The aluminum oxide film or aluminum film is deposited on the lower electrode via a plasma chemical vapor deposition, a thermal chemical vapor deposition, or a sputtering and then a heat treatment is performed thereon under non-oxygen atmosphere.
In performing the heat treatment of the aluminum oxide film under the non-oxygen ambient, the aluminum oxide film or the aluminum film is oxidized by oxygen supplied from a natural oxide film on the silicon, resulting in decreasing the oxidation of the silicon.
However, since the aluminum oxide film is subjected to the heat treatment under the non-oxygen ambient, a supplied amount of oxygen is insufficient. Accordingly, there is a problem in that a crystal structure of Al2O3 is unstable, causing poor leakage current characteristics.